US10522299B2 - Negative electrode active material for power storage device - Google Patents

Negative electrode active material for power storage device Download PDF

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US10522299B2
US10522299B2 US15/742,047 US201615742047A US10522299B2 US 10522299 B2 US10522299 B2 US 10522299B2 US 201615742047 A US201615742047 A US 201615742047A US 10522299 B2 US10522299 B2 US 10522299B2
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negative
active material
electrode active
discharge
power storage
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Hideo Yamauchi
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Nippon Electric Glass Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/04—Hybrid capacitors
    • H01G11/06—Hybrid capacitors with one of the electrodes allowing ions to be reversibly doped thereinto, e.g. lithium ion capacitors [LIC]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/46—Metal oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/54—Electrolytes
    • H01G11/58—Liquid electrolytes
    • H01G11/62—Liquid electrolytes characterised by the solute, e.g. salts, anions or cations therein
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5805—Phosphides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/13—Energy storage using capacitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

  • the present invention relates to negative-electrode active materials for use in power storage devices, such as a lithium-ion secondary battery, a sodium-ion secondary battery, and a hybrid capacitor, for use in portable electronic devices, electric vehicles, electric power tools, backup emergency power supplies, and so on.
  • power storage devices such as a lithium-ion secondary battery, a sodium-ion secondary battery, and a hybrid capacitor
  • NaTi 2 (PO 4 ) 3 and Na 3 Ti 2 (PO 4 ) 3 which are NASICON-type compounds, are proposed as negative-electrode active materials having relatively good cycle characteristics (see, for example, Patent Literature 1 and Non-Patent Literature 1).
  • the operating voltage of a power storage device is determined by the difference between the operating voltage of the positive electrode and the operating voltage of the negative electrode and becomes larger as the operating voltage of the negative electrode decreases.
  • NaTi 2 (PO 4 ) 3 or Na 3 Ti 2 (PO 4 ) 3 is used as the negative-electrode active material for the power storage device, the Ti 4+ /Ti 3+ reaction potential is very high, 2.2V (vs. Na/Na + ), so that the operating voltage of the negative electrode becomes high, which presents a problem that the operating voltage of the power storage device in which this negative-electrode active material is used becomes small.
  • the present invention has an object of providing a negative-electrode active material for a power storage device that has a low operating potential, can increase the operating voltage of the power storage device, and has excellent cycle characteristics.
  • a negative-electrode active material for a power storage device contains, in terms of % by mole of oxide, 1 to 95% TiO 2 and 5 to 75% P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O (where R′ represents at least one selected from Mg, Ca, Sr, Ba, and Zn) and contains 10% by mass or more amorphous phase.
  • R′ represents at least one selected from Mg, Ca, Sr, Ba, and Zn
  • the negative-electrode active material for a power storage device contains 10% by mass or more amorphous phase, it has excellent diffusivity of alkali ions, such as lithium ions or sodium ions and, therefore, facilitates insertion and extraction of alkali ions due to charge and discharge. As a result, the redox potential decreases and the operating voltage of the negative electrode can be decreased.
  • the content of the amorphous phase is as large as 10% by mass or more, the degree of freedom of composition is high, so that the increase in capacity and the decrease in voltage can be easily achieved.
  • the negative-electrode active material according to the present invention, a structure is formed in which Ti ions as an active material component are uniformly dispersed in an oxide matrix made of P 2 O 5 , SiO 2 , B 2 O 3 , Al 2 O 3 or R′O. Therefore, the volume change of Ti ions due to insertion and extraction of alkali ions can be restrained and the negative-electrode active material has excellent cycle characteristics.
  • the amorphous phase is likely to exist at the interface between the negative-electrode active material and the solid electrolyte.
  • the amorphous phase serves as a conducting path for alkali ions and therefore decreases the interfacial resistance between the active material crystal and the solid electrolyte, so that the discharge capacity and discharge voltage of the power storage device are likely to increase.
  • the amorphous phase also acts as a binder, the adhesive strength between the negative electrode layer and the solid electrolyte layer is increased.
  • the proportion of the amorphous phase is low, undesirable crystals may be precipitated depending on the composition. Such crystals cause an increase in the operating voltage of the negative-electrode active material, a decrease in rapid charge/discharge characteristics, and a decrease in cycle characteristics. Since the negative-electrode active material for a power storage device according to the present invention has a proportion of amorphous phase as high as 10% by mass or more, the precipitation of undesirable crystals can be inhibited.
  • the negative-electrode active material for a power storage device according to the present invention preferably further contains 1 to 70% R 2 O (where R represents at least one selected from Li, Na, and K).
  • the negative-electrode active material for a power storage device inserts and extracts alkali ions with charge and discharge, but some alkali ions may remain inserted in the negative-electrode active material without being extracted.
  • the remaining alkali ions lead to an irreversible capacity and cause a decrease in first discharge capacity.
  • an R 2 O is previously contained in the negative-electrode active material, which makes it difficult for alkali ions to be absorbed into the negative-electrode active material during the first charge and thus enables the first discharge capacity to increase.
  • the negative-electrode active material contains R 2 O, the alkali-ion conductivity increases and the operating voltage of the negative electrode is likely to decrease for the previously described reason.
  • the negative-electrode active material for a power storage device is preferably made of an amorphous phase.
  • the term “made of an amorphous phase” refers to the negative-electrode active material for which a diffraction line profile at 2 ⁇ values of 10 to 60° obtained by powder X-ray diffraction measurement (XRD) using CuK ⁇ rays includes a broad diffraction curve (amorphous halo) at 10 to 40° and no crystalline diffraction peak is found in the diffraction line profile. More specifically, the above term refers to the negative-electrode active material in which the proportion of the amorphous phase is approximately 100%.
  • the negative-electrode active material for a power storage device according to the present invention is suitable for use in a sodium-ion secondary battery.
  • a negative electrode material for a power storage device contains the above-described negative-electrode active material for a power storage device.
  • the present invention enables provision of a negative-electrode active material for a power storage device that has a low operating potential, can increase the operating voltage of the power storage device, and has excellent cycle characteristics.
  • FIG. 1 is a chart showing an XRD pattern of sample No. 6 which is a working example.
  • FIG. 2 is a chart showing an XRD pattern of No. 68 which is a working example.
  • FIG. 3 is a chart showing an XRD pattern of No. 69 which is a working example.
  • FIG. 4 is a graph showing first charge/discharge curves of a test cell for a sodium-ion secondary battery in which sample No. 6 as a working example is used.
  • FIG. 5 is a graph showing first charge/discharge curves of a test cell for a sodium-ion secondary battery in which sample No. 69 as a working example is used.
  • FIG. 6 is a graph showing first charge/discharge curves of a test cell for a sodium-ion secondary battery in which sample No. 70 as a working example is used.
  • FIG. 7 is a graph showing first charge/discharge curves of a test cell for a sodium-ion secondary battery in which sample No. 71 as a working example is used.
  • FIG. 8 is a graph showing first charge/discharge curves of a test cell for a sodium-ion secondary battery in which sample No. 72 as a working example is used.
  • FIG. 9 is a graph showing first charge/discharge curves of a test cell for a lithium-ion secondary battery in which sample No. 78 as a working example is used.
  • FIG. 10 is a graph showing first charge/discharge curves of a test cell for a sodium-ion secondary battery in which sample No. 87 as a comparative example is used.
  • FIG. 11 is a graph showing first charge/discharge curves of a test cell for a solid-state sodium-ion secondary battery in which sample No. 92 as a working example is used.
  • FIG. 12 is a graph showing first charge/discharge curves of a test cell for a solid-state sodium-ion secondary battery in which sample No. 93 as a working example is used.
  • a negative-electrode active material for a power storage device contains, in terms of % by mole of oxide, 1 to 95% TiO 2 and 5 to 75% P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O (where R′ represents at least one selected from Mg, Ca, Sr, Ba, and Zn).
  • TiO 2 is an active material component serving as sites where alkali ions are inserted and extracted.
  • the content of TiO 2 is preferably 1 to 95%, more preferably 5 to 72%, still more preferably 10 to 68%, yet still more preferably 12 to 58%, yet still more preferably 15 to 49%, and particularly preferably 15 to 39%. If the content of TiO 2 is too small, the discharge capacity per unit mass of the negative-electrode active material tends to be small and the charge/discharge efficiency during the first charge and discharge tends to decrease. On the other hand, if the content of TiO 2 is too large, the volume change of Ti ions due to insertion and extraction of alkali ions during charge and discharge become unable to be reduced, so that the cycle characteristics tend to decrease.
  • P 2 O 5 , SiO 2 , B 2 O 3 , Al 2 O 3 , and R′O have excellent alkali-ion conductivity and the effect of decreasing the operating voltage of the negative electrode. Furthermore, they have the effect of restraining the volume change of Ti ions during insertion and extraction of alkali ions to increase the cycle characteristics. Preferred among them are SiO 2 , B 2 O 3 , and Al 2 O 3 because they are excellent in the effect of decreasing the operating voltage.
  • the content of P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O is preferably 5 to 75%, more preferably 7 to 60%, still more preferably 10 to 50%, yet still more preferably 12 to 40%, and particularly preferably 20 to 35%.
  • Respective preferred ranges of contents of the components P 2 O 5 , SiO 2 , B 2 O 3 , Al 2 O 3 , and R′O are as follows.
  • the content of P 2 O 5 is preferably 5 to 75%, more preferably 7 to 60%, still more preferably 10 to 50%, yet still more preferably 12 to 40%, and particularly preferably 20 to 35%. If the content of P 2 O 5 is too small, the above effects are less likely to be achieved. On the other hand, if the content of P 2 O 5 is too large, the discharge capacity is likely to decrease and the water resistance is likely to decrease. Furthermore, when an aqueous electrode paste is prepared, undesirable other crystals are produced to break the P 2 O 5 network, so that the cycle characteristics are likely to decrease.
  • the content of SiO 2 is preferably 0 to 75%, more preferably 5 to 75%, still more preferably 7 to 60%, yet still more preferably 10 to 50%, yet still more preferably 12 to 40%, and particularly preferably 20 to 35%. If the content of SiO 2 is too large, the discharge capacity is likely to decrease.
  • the content of B 2 O 3 is preferably 0 to 75%, more preferably 5 to 75%, still more preferably 7 to 60%, yet still more preferably 10 to 50%, yet still more preferably 12 to 40%, and particularly preferably 20 to 35%. If the content of B 2 O 3 is too large, the discharge capacity is likely to decrease and the chemical durability is likely to decrease.
  • the content of Al 2 O 3 is preferably 0 to 75%, more preferably 5 to 70%, still more preferably 7 to 60%, yet still more preferably 10 to 50%, yet still more preferably 12 to 40%, and particularly preferably 15 to 35%. If the content of Al 2 O 3 is too large, the discharge capacity is likely to decrease.
  • the content of R′O is preferably 0 to 75%, more preferably 5 to 70%, still more preferably 7 to 60%, yet still more preferably 10 to 50%, yet still more preferably 12 to 40%, and particularly preferably 15 to 35%. If the content of R′O is too large, the discharge capacity is likely to decrease.
  • the content of each component of MgO, CaO, SrO, BaO, and ZnO is preferably 0 to 75%, more preferably 5 to 70%, still more preferably 7 to 60%, yet still more preferably 10 to 50%, yet still more preferably 12 to 40%, and particularly preferably 15 to 35%.
  • the negative-electrode active material preferably contains R 2 O (where R represents at least one selected from Li, Na, and K).
  • R 2 O is a component that makes it difficult for alkali ions to be absorbed into the negative-electrode active material during the first charge and thus increases the first discharge capacity.
  • R 2 O also has the effect of increasing alkali-ion conductivity to decrease the operating voltage of the negative electrode.
  • the content of R 2 O is preferably 1 to 70%, more preferably 5 to 60%, still more preferably 7 to 55%, yet still more preferably 10 to 53%, and particularly preferably 15 to 49%. If the content of R 2 O is too small, the above effects are less likely to be achieved.
  • the use of Li 2 O or Na 2 O having a small atomic weight is preferred because it can increase the content of active material component and Na 2 O present as a plentiful resource is particularly preferred.
  • the negative-electrode active material preferably contains Li 2 O.
  • the negative-electrode active material preferably contains Na 2 O.
  • the negative-electrode active material preferably contains K 2 O.
  • the molar ratio between the content of TiO 2 and the content of P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O is preferably 0.2 to 4, more preferably 0.3 to 3, still more preferably 0.4 to 2.5, and particularly preferably 0.5 to 2. If TiO 2 /(P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O) is too small, the amount of active material component becomes small, so that the discharge capacity is likely to decrease.
  • alkali ions inserted during the first charge are likely to be absorbed in an oxide matrix made of P 2 O 5 , SiO 2 , B 2 O 3 , Al 2 O 3 or R′O, so that the first charge/discharge efficiency tends to decrease.
  • TiO 2 /(P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O) is too large, the oxide matrix made of P 2 O 5 , SiO 2 , B 2 O 3 , Al 2 O 3 or R′O becomes unable to reduce the volume change of Ti ions, so that the cycle characteristics tend to decrease.
  • the molar ratio between the content of R 2 O and the content of (P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O) (R 2 O/(P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O)) is preferably 0.03 to 2.5, more preferably 0.1 to 2.3, still more preferably 0.3 to 2.2, and particularly preferably 0.5 to 2.1.
  • R 2 O/(P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O) is too small, the content of alkali ions contained in the oxide matrix made of P 2 O 5 , SiO 2 , B 2 O 3 , Al 2 O 3 or R′O decreases, so that the ion conductivity is likely to decrease. As a result, the redox potential during charge and discharge increases, so that the operating voltage of the power storage device is likely to decrease. Furthermore, alkali ions inserted during the first charge are likely to be absorbed in the oxide matrix made of P 2 O 5 , SiO 2 , B 2 O 3 , Al 2 O 3 or R′O, so that the first charge/discharge efficiency tends to decrease.
  • various components can be contained in the negative-electrode active material without impairing the effects of the present invention.
  • various components can be contained in the negative-electrode active material without impairing the effects of the present invention.
  • oxides CuO, SnO, Bi 2 O 3 , GeO 2 , ZrO 2 , V 2 O 5 , Nb 2 O 5 , Fe 2 O 3 or Sb 2 O 5 can be contained in the negative-electrode active material.
  • V 2 O 5 , Nb 2 O 5 , and Fe 2 O 3 are preferred because they serve as active material components.
  • the content of the above components is, in total, preferably 0 to 40%, more preferably 0.1 to 30%, and particularly preferably 0.5 to 20%.
  • the negative-electrode active material according to the present invention contains an amorphous phase in an amount of 10% by mass or more, preferably 30% by mass or more, more preferably 50% by mass or more, still more preferably 80% by mass or more, yet still more preferably 90% by mass or more, yet still more preferably 95% by mass or more, yet still more preferably 99% by mass or more, particularly preferably 99.9% by mass or more, and most preferably the negative-electrode active material is made of an amorphous phase. If the content of amorphous phase is too small, the alkali-ion conductivity is likely to decrease.
  • the content of amorphous phase can be determined by using a diffraction line profile at 2 ⁇ values of 10 to 60° obtained by powder X-ray diffraction measurement using CuK ⁇ rays and making a peak separation of the profile into crystalline diffraction lines and an amorphous halo.
  • the background is subtracted from the diffraction line profile to obtain a total scattering curve
  • a broad diffraction curve (amorphous halo) at 10 to 45° is peak-separated from the total scattering curve and integrated
  • the obtained integrated intensity of the halo is represented as Ia
  • crystalline diffraction lines of each of crystalline phases detected at 10 to 60° are peak-separated from the total scattering curve and integrated
  • the sum of the obtained integrated intensities of the crystalline diffraction lines is represented as Ic.
  • the content Xc of crystals and the content Xa of amorphous phase can be determined from the following equations.
  • Xc [ Ic /( Ic+Ia )] ⁇ 100(%)
  • Xa 100 ⁇ Xc (%)
  • the negative-electrode active material for a power storage device can be manufactured by formulating raw material powders to give a desired composition and using the obtained raw material powders to subject them to a melting and rapid cooling process, a sol-gel process, a chemical vapor synthesis process, such as spraying of a mist of raw material powder solution into flame, a mechanochemical process or other processes.
  • a composition that is difficult to vitrify for example, a composition having a large content of TiO 2
  • an usual melting and rapid cooling process may not be able to form a desired amorphous body and thus may not be able to provide a homogeneous negative-electrode active material.
  • melt-solidified body obtained by the usual melting and rapid cooling process be first made into powder form and then be sprayed into flame to be melted again and rapidly cooled. In this manner, even a composition that is difficult to vitrify as described above can be easily made amorphous.
  • the negative-electrode active material obtained by the above methods is, as necessary, ground or classified in order to obtain powder having a desired size.
  • a mortar, a ball mill, a vibrating ball mill, a satellite ball mill, a planetary ball mill, a jet mill or other means can be used.
  • classification, sieving, centrifugation, air classification or other methods can be used.
  • its average particle size is preferably 0.1 to 20 ⁇ m, more preferably 0.2 to 15 ⁇ m, still more preferably 0.3 to 10 ⁇ m, and particularly preferably 0.5 to 5 ⁇ m.
  • its maximum particle size is preferably 150 ⁇ m or less, more preferably 100 ⁇ m or less, still more preferably 75 ⁇ m or less, and particularly preferably 55 ⁇ m or less.
  • the average particle size or maximum particle size of the negative-electrode active material is too large, this results in an inability to reduce the volume change of the negative-electrode active material due to insertion and extraction of alkali ions during charge and discharge, so that the negative-electrode active material is likely to peel off the current collector and the cycle characteristics tend to significantly decrease.
  • the average particle size is too small, the dispersed state of powder in the negative-electrode active material when produced in paste form is likely to be poor. As a result, it becomes necessary to increase the amounts of binder and solvent added or the applicability becomes poor, so that a uniform electrode formation tends to become difficult.
  • the average particle size and the maximum particle size refer to a median primary particle diameter D50 (diameter at 50% cumulative volume) and a median primary particle diameter D90 (diameter at 90% cumulative volume), respectively, and are values measured by a laser diffraction particle size distribution measurement device.
  • the specific surface area of the negative-electrode active material in powder state measured by the BET method is preferably 0.1 to 20 m 2 /g, more preferably 0.15 to 15 m 2 /g, and particularly preferably 0.2 to 10 m 2 /g. If the specific surface area of the negative-electrode active material is too small, alkali ions cannot be rapidly inserted and extracted, so that the charge/discharge time tends to be long. On the other hand, if the specific surface area of the negative-electrode active material is too large, the dispersed state of powder in the negative-electrode active material when produced in paste form is likely to be poor. As a result, it becomes necessary to increase the amounts of binder and solvent added or the applicability becomes poor, so that a uniform electrode formation tends to become difficult.
  • the negative-electrode active material for a power storage device according to the present invention is preferably coated or mixed with electrically conductive carbon to be given electrical conductivity.
  • electrically conductive carbon By coating the surface of the negative-electrode active material with electrically conductive carbon, the electronic conductivity becomes high, so that the rapid charge/discharge characteristics are likely to increase.
  • the electrically conductive carbon that can be used include highly electrically conductive carbon blacks, such as acetylene black and Ketjenblack, carbon powders, such as graphite, and carbon fibers. Preferred among them is acetylene black because of its high electronic conductivity.
  • An example of a method for mixing the negative-electrode active material and the electrically conductive carbon while grinding them is a method in which a general grinder is used, such as a mortar, a mortar mixer, a ball mill, an attritor, a vibrating ball mill, a satellite ball mill, a planetary ball mill, a jet mill or a bead mill. Preferred among them is the use of a planetary ball mill.
  • the planetary ball mill has a structure in which a disk rotates on its axis while pots thereon rotate on their own axises, so that very high impact energy can be efficiently produced to enable homogeneous dispersion of the electrically conductive carbon into the negative-electrode active material.
  • the method for imparting the negative-electrode active material electrical conductivity is a method of mixing a negative-electrode active material in powder state and an organic compound and then firing the mixture in an inert atmosphere or a reductive atmosphere to carbonize the organic compound, thus coating the surface of the negative-electrode active material with the electrically conductive carbon.
  • the firing temperature is preferably the crystallization temperature of the negative-electrode active material or below and particularly preferably (the crystallization temperature minus 30° C.) or below.
  • Any organic compound may be used as far as it can stay as carbon after being subjected to heat treatment and examples include glucose, citric acid, ascorbic acid, phenolic resin, and a surfactant. Particularly preferred is a surfactant because of its ease of adsorption on the surface of the negative-electrode active material.
  • the surfactant may be any of a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and a non-ionic surfactant, but particularly preferred is a non-ionic surfactant because of its excellent adsorbability on the surface of the negative-electrode active material.
  • the content of the electrically conductive carbon is, per 100 parts by mass of negative-electrode active material, preferably 0.01 to 20 parts by mass, more preferably 0.03 to 15 parts by mass, still more preferably 0.05 to 12 parts by mass, and particularly preferably 0.07 to 10 parts by mass. If the content of electrically conductive carbon is too small, the negative-electrode active material is insufficiently coated and tends to be less electronically conductive. On the other hand, if the carbon content is too large, the proportion of negative-electrode active material in the negative electrode material becomes small, so that the discharge capacity is likely to decrease.
  • the thickness of the electrically conductive carbon coating formed on the surface of the negative-electrode active material is preferably 1 to 100 nm and particularly preferably 5 to 80 nm. If the thickness of the electrically conductive carbon coating is too small, the coating may be lost in the charging/discharging process to deteriorate the battery characteristics. On the other hand, if the thickness of the electrically conductive carbon coating is too large, the discharge capacity and operating voltage of the power storage device are likely to decrease.
  • the ratio (D/G) of a peak intensity D between 1300 and 1400 cm ⁇ 1 to a peak intensity G between 1550 and 1650 cm ⁇ 1 , both measured by Raman spectroscopy is preferably 1 or less and particularly preferably 0.8 or less
  • the ratio (F/G) of a peak intensity F between 800 to 1100 cm ⁇ 1 to the peak intensity G is preferably 0.5 or less and particularly preferably 0.1 or less.
  • the peak intensity G originates from crystalline carbon and the peak intensity D originates from amorphous carbon.
  • the peak intensity ratio D/G is smaller, this means that the electrically conductive carbon coating is more crystalline, and the electronic conductivity tends to be higher.
  • the peak intensity F originates from the components of the negative-electrode active material. Therefore, as the peak intensity ratio F/G is smaller, this means that a higher proportion of the surface of the negative-electrode active material is covered with crystalline, electrically conductive carbon coating, and the electronic conductivity tends to be higher.
  • the negative-electrode active material for a power storage device has a tapped density of preferably 0.3 g/ml or more and particularly preferably 0.5 g/ml or more. If the tapped density of the negative-electrode active material is too small, the electrode density becomes small, so that the discharge capacity per unit volume of the electrode tends to decrease.
  • the upper limit of the tapped density is a value approximately corresponding to the true specific gravity of the negative-electrode active material, but is, in consideration of powder aggregation, actually 5 g/ml or less and particularly 4 g/ml or less. Note that in the present invention the tapped density refers to a value measured under conditions of a tapping stroke of 10 mm, a number of taps of 250, and a tapping rate of two taps per second.
  • the negative-electrode active material for a power storage device according to the present invention can be used as a negative electrode material for a power storage device by adding a binder and a conductive aid to make the negative-electrode active material into paste form.
  • the binder is a component to be added to the negative-electrode active material in order to bind the negative-electrode active material particles together or bind the negative-electrode active material and the solid electrolyte to prevent the negative-electrode active material from peeling off the negative electrode due to a volume change during charge and discharge.
  • binder examples include thermoplastic straight-chain polymers, such as polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) (PVDF), fluorine-containing rubbers, and styrene-butadiene rubber (SBR); thermosetting resins, such as thermosetting polyimide, polyamide-imide, polyamide, phenolic resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, and polyurethane; cellulose derivatives, such as carboxymethyl cellulose (including salts of carboxymethyl cellulose, such as sodium carboxymethyl cellulose, the same applies hereafter), hydroxypropylmethyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, ethyl cellulose, and hydroxymethyl cellulose; and water-soluble polymers, such as polyvinyl alcohol, polyacrylamide, polyvinyl pyrrolidone, and their copolymers.
  • PTFE polytetrafluoroethylene
  • PVDF poly(
  • thermosetting resins, cellulose derivatives, and water-soluble polymers are preferred because of their excellent binding properties and thermosetting polyimide or carboxymethyl cellulose is more preferred because of their industrially widespread use.
  • carboxymethyl cellulose is most preferred because it is inexpensive and does not need any organic solvent for preparation of a paste having a low environmental burden.
  • binders may be used singly or in a mixture of two or more of them.
  • the conductive aid examples include highly electrically conductive carbon blacks, such as acetylene black and Ketjenblack, carbon powders, such as graphite, and carbon fibers.
  • the negative-electrode active material for a power storage device according to the present invention can also be used as a composite material as an electrode by mixing with a below-described alkali-ion conductive solid electrolyte.
  • the above negative electrode material for a power storage device can be used as a negative electrode for a power storage device by applying the negative electrode material for a power storage device to the surface of a metal foil or the like serving as a current collector or by using the negative electrode material for a power storage device to form a negative electrode layer and then forming a metal thin film or the like on the surface of the negative electrode layer.
  • the negative electrode for a power storage device can be used as a power storage device by combining with a separately prepared positive electrode for a power storage device and an electrolyte.
  • An aqueous electrolyte, a nonaqueous electrolyte or a solid electrolyte can be used as the electrolyte.
  • the aqueous electrolyte is made by dissolving an electrolyte salt in water.
  • alkali ions to be supplied from the positive electrode are lithium ions
  • examples of the electrolyte salt include LiNO 3 , LiOH, LiF, LiCl, LiBr, LiI, LiClO 4 , Li 2 SO 4 , CH 3 COOLi, LiBF 4 , and LiPF 6 .
  • examples of the electrolyte salt include NaNO 3 , Na 2 SO 4 , NaOH, NaCl, and CH 3 COONa.
  • examples of the electrolyte salt include KNO 3 , KOH, KF, KCl, KBr, KI, KClO 4 , K 2 SO 4 , CH 3 COOK, KBF 4 , and KPF 6 . These electrolyte salts may be used singly or in a mixture of two or more of them.
  • the electrolyte salt concentration is appropriately adjusted, generally, within a range of not less than 0.1 M and not more than the saturation concentration.
  • the nonaqueous electrolyte contains: an organic solvent and/or an ionic liquid both of which are nonaqueous solvents; and an electrolyte salt dissolved in the nonaqueous solvent.
  • organic solvent the organic solvent, the ionic liquid, and the electrolyte salt are as follows. Note that the characters in [ ] after the below-mentioned compound names indicate abbreviations.
  • organic solvent examples include propylene carbonate [PC], ethylene carbonate [EC], 1,2-dimethoxyethane [DME], ⁇ -butyrolactone [GBL], tetrahydrofuran [THF], 2-methyltetrahydrofuran [2-MeHF], 1,3-dioxolan, sulfolane, acetonitrile [AN], diethyl carbonate [DEC], dimethyl carbonate [DMC], methylethyl carbonate [MEC], and dipropyl carbonate [DPC].
  • PC propylene carbonate
  • EC ethylene carbonate
  • DME 1,2-dimethoxyethane
  • GBL ⁇ -butyrolactone
  • THF tetrahydrofuran
  • 2-MeHF 2-methyltetrahydrofuran
  • 1,3-dioxolan 1,3-dioxolan
  • sulfolane examples include acetonitrile [AN], diethyl carbonate [DEC
  • the ionic liquid examples include: aliphatic quaternary ammonium salts, such as N,N,N-trimethyl-N-propyl ammonium bis(trifluoromethanesulfonyl)imide [TMPA-TFSI], N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide [PP13-TFSI], N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide [P13-TFSI], and N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide [P14-TFSI]; and quaternary alkylimidazolium salts, such as 1-methyl-3-ethylimidazolium tetrafluoroborate [EMIBF4], 1-methyl-3-ethylimidazolium bis(trifluoromethanesulfony
  • electrolyte salt examples include lithium salts, sodium salts, and potassium salts of PF 6 ⁇ , BF 4 ⁇ , (CF 3 SO 2 ) 2 N ⁇ [TFSI]. CF 3 SO 3 ⁇ [TFS], (C 2 F 5 SO 2 ) 2 N ⁇ [BETI], ClO 4 ⁇ , AsF 6 ⁇ , SbF 6 ⁇ , B(C 2 O 4 ) 2 ⁇ [BOB], BF 2 OCOOC(CF 3 ) 3 ⁇ [B(HHIB)], and so on. These electrolyte salts may be used singly or in a mixture of two or more of them.
  • lithium salts, sodium salts, and potassium salts of PF 6 ⁇ and BF 4 ⁇ are inexpensive.
  • the electrolyte salt concentration is appropriately adjusted, generally, within a range of not less than 0.5 M and not more than 3 M.
  • the nonaqueous electrolyte may contain an additive, such as vinylene carbonate [VC], vinylene acetate [VA], vinylene butyrate, vinylene hexanoate, vinylene crotonate or catechol carbonate.
  • VC vinylene carbonate
  • VA vinylene acetate
  • VA vinylene butyrate
  • vinylene hexanoate vinylene crotonate
  • catechol carbonate a protective film
  • the amount of additive is, per 100 parts by mass of nonaqueous electrolyte, preferably 0.1 to 3 parts by mass and particularly preferably 0.5 to 1 parts by mass. If the amount of additive is too small, the above effect is less likely to be achieved. On the other hand, even if the amount of additive is too large, improvement in the above effect is less likely to be achieved.
  • examples of the solid electrolyte include lithium ⁇ -alumina, lithium ⁇ ′′-alumina, Li 2 S—P 2 S 5 glass or crystallized glass, Li 1+x AL x Ge 2 ⁇ x (PO 4 ) 3 crystal or crystallized glass, Li1 4 Al0.
  • examples of the solid electrolyte include sodium ⁇ -alumina, sodium ⁇ ′′-alumina, Na 1+x Zr 2 Si x P 3 ⁇ x O1 2 crystal or crystallized glass, Na 3.12 Si 2 Zr 1.88 Y 0.12 PO 12 crystal or crystallized glass, and Na 5.9 Sm 0.6 Al 0.1 P 0.3 Si 3.6 O 9 crystallized glass.
  • examples of the electrolyte salt include potassium ⁇ -alumina and potassium ⁇ ′′-alumina.
  • nonaqueous electrolytes and solid electrolytes are preferred because of their wide potential windows.
  • solid electrolytes having alkali-ion conductivity have wide potential windows and, therefore, produce little gas due to electrolyte decomposition during charge and discharge, so that the safety of the power storage device can be increased.
  • a separator is preferably provided between the electrodes.
  • the separator is made of a material having insulation properties and specific examples of the material that can be used include porous film or non-woven fabric obtained from a polymer, such as polyolefin, cellulose, polyethylene terephthalate or vinylon; non-woven glass fabric containing glass fibers; glass cloth in which glass fibers are woven, and film-like glass.
  • the type of positive-electrode active material for use in the positive electrode is not particularly limited and can be appropriately selected depending on the type or so on of the desired power storage device.
  • examples of the positive-electrode active material include NaFeO 2 , NaNiO 2 , NaCoO 2 , NaMnO 2 , NaVO 2 , Na(Ni x Mn 1 ⁇ x )O 2 , Na(Fe x Mn 1 ⁇ x )O 2 (where 0 ⁇ x ⁇ 1), NaVPO 4 , Na 2 FeP 2 O 7 , and Na 3 V 2 (PO 4 ) 3 .
  • examples of the positive-electrode active material include LiCoO 2 , LiNiO 2 , LiCo 1/3 Ni 1/3 Mn 1/3 O 2 , LiVO 2 , LiCrO 2 , LiMn 2 O 4 , LiFePO 4 , and LiMnPO 4 .
  • the negative-electrode active material may contain an oxide of lithium, sodium or potassium, an oxide containing Ti 4+ , Ti 3+ or Ti 2+ , or like substances.
  • the negative-electrode active material for a power storage device contains, at the completion of discharge, in terms of % by mole of oxide, 1 to 75% R 2 O (where R represents at least one selected from Li, Na, and K), 0.5 to 59% TiO 2 , and 10 to 65% P 2 O 5 +SiO 2 +B 2 O 3 +Al 2 O 3 +R′O (where R′ represents at least one selected from Mg, Ca, Sr, Ba, and Zn).
  • the power storage device is an alkali-ion secondary battery, such as a lithium-ion secondary battery or a sodium-ion secondary battery
  • the present invention is not limited to them and is also applicable to, for example, a hybrid capacitor in which a negative-electrode active material for use in a lithium-ion secondary battery, a sodium-ion secondary battery or like battery is combined with a positive electrode material for a nonaqueous electric double layer capacitor.
  • Each of a lithium-ion capacitor and a sodium-ion capacitor which are hybrid capacitors is a type of asymmetric capacitor having different charge/discharge principles between the positive and negative electrodes.
  • the lithium-ion capacitor has a structure in which a negative electrode for a lithium-ion secondary battery is combined with a positive electrode for an electric double layer capacitor.
  • the sodium-ion capacitor has a structure in which a negative electrode for a sodium-ion secondary battery is combined with a positive electrode for an electric double layer capacitor.
  • the positive electrode has an electric double layer formed on the surface thereof and is charged and discharged using a physical action (electrostatic action), while the negative electrode is charged and discharged, like the previously described lithium-ion secondary battery or sodium-ion secondary battery, by a chemical reaction (insertion and extraction) of lithium ions or sodium ions.
  • a positive-electrode active material which is made of, for example, carbonaceous powder having a high specific surface area, such as activated charcoal, polyacene or mesophase carbon.
  • the negative electrodes thereof the negative-electrode active material according to the present invention can be used.
  • the negative-electrode active material according to the present invention When the negative-electrode active material according to the present invention is used in the lithium-ion capacitor or the sodium-ion capacitor, it is necessary to previously insert lithium ions or sodium ions and electrons in the negative-electrode active material.
  • the means for implementing this is not particularly limited.
  • a metallic lithium electrode or a metallic sodium electrode which serves as a supply source of lithium ions or sodium ions and electrons, may be placed in a capacitor cell and brought into contact directly or through a conductor with a negative electrode containing the negative-electrode active material according to the present invention.
  • the negative-electrode active material may be incorporated into a capacitor cell.
  • Tables 1 to 14 show working examples (Nos. 1 to 86) of the present invention and comparative examples (Nos. 87 and 88).
  • the melt-solidified body was ground with a ball mill and the obtained powder was sprayed directly into burner flame, then rapidly cooled, and further ground with a jet mill to obtain a negative-electrode active material in powder state having an average particle size of 2 ⁇ m.
  • the obtained negative-electrode active material was coated with carbon in the following manner.
  • the XRD patterns of sample Nos. 6, 68, and 69 are shown in FIGS. 1 to 3 , respectively.
  • FIGS. 1 and 2 in each of the XRD patterns of samples Nos. 6 and 68, an amorphous halo was detected but no crystalline diffraction line was detected.
  • an amorphous halo was likewise detected but no crystalline diffraction line was likewise detected.
  • FIG. 3 in the XRD pattern of sample No. 69, an amorphous halo and crystalline diffraction lines attributed to Na 3 PO 4 were detected.
  • the content of the amorphous phase was determined by the previously described method. Moreover, also in each of the XRD patterns of samples Nos. 71, 73, and 74, an amorphous halo and crystalline diffraction lines were likewise detected. The contents of these amorphous phases were determined.
  • samples Nos. 1 to 67, 87, and 88 electrically conductive carbon black (Super C65 manufactured by Timcal) as a conductive aid and poly(vinylidene fluoride) as a binder were weighed and mixed with the negative-electrode active material powder to reach a ratio of negative-electrode active material powder to conductive aid to binder of 92:3:5 (mass ratio) and the mixture was dispersed into N-methylpyrrolidinone (NMP), followed by well stirring with a planetary centrifugal mixer to forma slurry, thus obtaining a negative electrode material.
  • NMP N-methylpyrrolidinone
  • the negative-electrode active material powder, the conductive aid, and the binder were weighed and mixed to reach a ratio of negative-electrode active material powder to conductive aid to binder of 85:5:10 (mass ratio) and the mixture was processed in the same manner as above, thus obtaining a negative electrode material.
  • the obtained negative electrode material was coated on a 20- ⁇ m thick copper foil serving as a negative electrode current collector using a doctor blade with a gap of 125 ⁇ m, and the negative electrode material coated on the copper foil was vacuum-dried by a dryer at 70° C. and then pressed by passing it between a pair of rotating rollers to obtain an electrode sheet.
  • This electrode sheet was punched out into an 11-mm diameter disc by an electrode cutting machine and the disc was dried at a temperature of 150° C. for eight hours under reduced pressure, thereby obtaining a circular negative electrode.
  • a test cell for a sodium-ion secondary battery was produced in the following manner.
  • the negative electrode obtained in the above manner was placed, with its copper foil surface down, on a lower lid of a coin cell, and a separator formed of a 16-mm diameter polypropylene porous film dried at 70° C. for eight hours under reduced pressure and a metallic sodium layer as a counter electrode were laminated on the negative electrode, thus producing a test cell.
  • a 1M NaPF 6 solution/EC:DEC 1:1 (where EC is ethylene carbonate and DEC is diethyl carbonate) was used as an electrolytic solution.
  • the assembly of the test cell was conducted in an environment at the dew-point temperature minus 70° C. or below.
  • a test cell for a lithium-ion secondary battery was produced in the following manner.
  • the negative electrode obtained in the above manner was placed, with its copper foil surface down, on a lower lid of a coin cell, and a separator formed of a 16-mm diameter polypropylene porous film dried at 70° C. for eight hours under reduced pressure and a metallic lithium layer as a counter electrode were laminated on the negative electrode, thus producing a test cell.
  • a 1M LiPF 6 solution/EC:DEC 1:1 (where EC is ethylene carbonate and DEC is diethyl carbonate) was used as an electrolytic solution.
  • the assembly of the test cell was conducted in an environment at the dew-point temperature minus 50° C. or below.
  • the test cell for a sodium-ion secondary battery was CC (constant-current) charged at 30° C. from an open circuit voltage to 0.5 V and its amount of electricity charged to the negative-electrode active material per unit mass (first charge capacity) was determined.
  • the test cell was CC discharged from 0.5 V to 2.5 V and its amount of electricity discharged from the negative-electrode active material per unit mass (first discharge capacity) was determined.
  • the first charge capacity was determined by charging them from the open circuit voltage to 0.01 V and, next, the first discharge capacity was determined by CC discharging them from 0.01 V to 2.5 V.
  • the C rate was 0.1 C.
  • the test cell for a lithium-ion secondary battery was CC (constant-current) charged at 30° C. from an open circuit voltage to 1.5 V and its amount of electricity charged to the negative-electrode active material per unit mass (first charge capacity) was determined.
  • the test cell was CC discharged from 1.5 V to 3.2 V and its amount of electricity discharged from the negative-electrode active material per unit mass (first discharge capacity) was determined.
  • the first charge capacity was determined by charging them from the open circuit voltage to 0.01 V and, next, the first discharge capacity was determined by CC discharging them from 0.01 V to 2.5 V.
  • the C rate was 0.1 C.
  • samples Nos. 87 and 88 which are comparative examples, the discharge voltage and discharge capacity retention in each of the test cells for sodium-ion secondary batteries were 2.15 V or more and 69% or less, respectively, the discharge voltage and discharge capacity retention in each of the test cells for lithium-ion secondary batteries were 2.59 V or more and 69% or less, respectively, and the comparative examples were poorer in these characteristics as compared to the working examples.
  • Tables 15 and 16 show working examples (Nos. 89 to 93) of the present invention.
  • the coarse glass powder was ground, using ethanol as a grinding aid, for 80 hours with a ball mill using a 3-mm diameter ZrO 2 ball, thus obtaining glass powder (negative-electrode active material precursor powder) having an average particle size of 0.6 ⁇ m.
  • the glass powder was confirmed to be amorphous.
  • a Li 2 O-stabilized ⁇ ′′ alumina having a composition formula of Na 1.6 Li 0.34 Al 10.66 O 17 (manufactured by Ionotec Ltd.) was processed by dry grinding to a thickness of 0.2 mm, thus obtaining a solid electrolyte sheet. Furthermore, solid electrolyte powder (having an average particle size of 13 ⁇ m) was separately prepared by grinding the obtained solid electrolyte sheet with a planetary ball mill and passing the ground product through a sieve with 10- ⁇ m openings.
  • Sodium carbonate (Na 2 CO 3 ), aluminum oxide (Al 2 O 3 ), and magnesium oxide (MgO) were used as raw materials, powders of these raw materials were formulated to give a composition of, in % by mole, 13.0% Na 2 O, 80.2% Al 2 O 3 , and 6.8% MgO, and the mixture was ground and mixed in ethanol for 10 hours with a ball mill using a 5-mm diameter Al 2 O 3 ball.
  • the obtained powder was formed into a 0.2-mm thick sheet, then isostatically pressed at a pressure of 40 MPa, and heat-treated in an air atmosphere at 1640° C. for an hour to obtain a solid electrolyte sheet made of MgO-stabilized ⁇ ′′ alumina.
  • solid electrolyte powder (having an average particle size of 12 ⁇ m) was separately prepared by grinding the obtained solid electrolyte sheet with a planetary ball mill and passing the ground product through a sieve with 10- ⁇ m openings.
  • powder X-ray diffraction pattern of the obtained solid electrolyte powder was checked, diffraction lines originating from ((Al 10.32 Mg 0.68 O 16 ) (Na 1.68 O)) which is a trigonal crystal belonging to space group R-3m were confirmed.
  • Sodium metaphosphate (NaPO 3 ), yttria-stabilized zirconia ((ZrO 2 ) 0.97 (Y 2 O 3 ) 0.03 ), sodium carbonate (Na 2 CO 3 ), and silicon oxide (SiO 2 ) were used as raw materials, powders of these raw materials were formulated to give a composition of, in % by mole, 25.3% Na 2 O, 31.6% ZrO 2 , 1.0% Y 2 O 3 , 8.4% P 2 O 5 , and 33.7% SiO 2 , and the mixture was ground and mixed in ethanol for 10 hours with a ball mill using a 5-mm diameter Al 2 O 3 ball.
  • the obtained powder was formed into a 0.2-mm thick sheet, then isostatically pressed at a pressure of 40 MPa, and heat-treated in an air atmosphere at 1250° C. for two hours to obtain a solid electrolyte sheet made of NASICON crystal.
  • solid electrolyte powder (having an average particle size of 12 ⁇ m) was separately prepared by grinding the obtained solid electrolyte sheet with a planetary ball mill and passing the ground product through a sieve with 10- ⁇ m openings.
  • powder X-ray diffraction pattern of the solid electrolyte crystal was checked, diffraction lines originating from (Na 3.05 Zr 2 Si 2.05 P 0.95 O 12 ) which is a trigonal crystal belonging to space group R-3c were confirmed.
  • the negative-electrode active material precursor powder and solid electrolyte powder obtained in the above manners, and acetylene black (SUPER C65 manufactured by TIMICAL) as electrically conductive carbon were weighed in each ratio described in Tables 15 and 16 and mixed at 300 rpm for 30 minutes using a planetary ball mill. Added to 100 parts by mass of the obtained mixture powder were 10 parts by mass of polypropylene carbonate (manufactured by Sumitomo Seika Chemicals Co., Ltd.) and additionally 30 parts by mass of N-methylpyrrolidinone. The mixture was fully stirred with a planetary centrifugal mixer to form a slurry.
  • polypropylene carbonate manufactured by Sumitomo Seika Chemicals Co., Ltd.
  • the obtained slurry was applied, with an area of 1 cm 2 and a thickness of 80 ⁇ m, to one side of the solid electrolyte sheet described in Tables 15 and 16 and then dried at 70° C. for three hours.
  • the obtained product was put into a carbon container and fired in a nitrogen atmosphere at 650° C. (600° C. as for No. 92) for an hour to soften and fluidize the negative-electrode active material precursor powder and thermally fuse the materials together, thus forming a negative electrode layer. All the above operations were conducted in an environment at a temperature of the dew point minus 50° C. or below.
  • a current collector formed of a 300-nm thick gold electrode was formed on the surface of the negative electrode layer using a sputtering device (SC-701AT manufactured by Sanyu Electron Co., Ltd.). Furthermore, in an argon atmosphere at the dew point minus 70° C. or below, a metallic sodium layer serving as a counter electrode was pressure-bonded to the surface of the solid electrolyte layer opposite to the surface thereof on which the negative electrode layer was formed. The obtained laminate was placed on a lower lid of a coin cell and covered with an upper lid to produce a CR2032-type test cell.
  • SC-701AT manufactured by Sanyu Electron Co., Ltd.
  • the produced test cell was CC (constant-current) charged at 60° C. from an open circuit voltage to 0.01 V and its first charge capacity was determined.
  • the test cell was CC discharged from 0.01 V to 2.5 V and its first discharge capacity was determined.
  • the C rate was 0.01 C and “Discharge Capacity Retention” was evaluated as a rate of the 10th cycle discharge capacity to the first discharge capacity.
  • Tables 15 and 16 Furthermore, the first charge/discharge curves of the test cells for solid-state sodium-ion secondary batteries using samples Nos. 92 and 93 are shown in FIGS. 11 and 12 .
  • each of samples Nos. 89 to 93 exhibited an excellent discharge voltage of 1.4 V or less and an excellent discharge capacity retention of 98% or more.
  • the negative-electrode active material for a power storage device according to the present invention is suitable for power storage devices used in portable electronic devices, electric vehicles, electric power tools, backup emergency power supplies, and so on.

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